Juices and other acidic juice-like beverages are popular commercial products. Consumer demand for nutritional healthy beverages has led to the development of nutritional juice or juice-like beverages containing protein. The protein provides nutrition in addition to the nutrients provided by the components of the beverage. Recently it has been discovered that certain proteins have specific health benefits beyond providing nutrition. For example, soy protein has been recognized by the United States Food and Drug Administration as being effective to lower blood cholesterol concentrations in conjunction with a healthy diet. In response, there has been a growing consumer demand for acidic juice-like beverages containing proteins that provide such specific health benefits.
A hurdle to adding protein to acidic beverages, however, is the relative insolubility of proteins in an aqueous acidic environment. Most commonly used proteins, such as soy proteins and casein, have an isoelectric point at an acidic pH. Thus, the proteins are least soluble in an aqueous liquid at or near the pH of acidic beverages. For example, soy protein has an isoelectric point at pH 4.5 and casein has an isoelectric point at a pH of 4.7, while most common juices have a pH in the range of 3.7 to 4.0. As a result, protein tends to settle out as a sediment in an acidic protein-containing beverage—an undesirable quality in a beverage.
Protein stabilizing agents that stabilize proteins as a suspension in an aqueous acidic environment are used to overcome the problems presented by protein insolubility. Pectin is a commonly used protein stabilizing agent. Pectin, however, is an expensive food ingredient, and manufacturers of aqueous acidic beverages containing protein desire less expensive stabilizers, where the amount of required pectin is either reduced or removed in favor of less expensive stabilizing agents.
The majority of protein based juice drinks are made from dry protein sources including casein, whey and soy protein. The advantages of a dry protein source are the small storage volume, the ease of shipment and the ease of handling during production, since the protein is spray dried to obtain a powder. However, dry protein powders undergo high heat treatment during the spray drying process and this in turn leads to a loss of some functionality, especially on solubility in the juice drink. Solubility is a key element for a stable acid protein juice drink.
Soy milk is an alternative raw material that could be used in juice drinks, however, the low protein content of soy milk coupled with its beany flavor, limit the application of soy milk in juice drinks.
The advantage of this invention is that while a soy protein is employed for acid beverages, the soy protein is not subjected to the spray drying step. Liquid soy protein that is obtained prior to the spray drying process has a high protein concentration and full functionality. As such, it can be used in acid beverages that would have a high degree of stability over a long period of storage time at ambient temperature. A liquid soy protein will retain all its functionality, since there is no phase transition generated by the spray drying process. The spray drying step tends to decrease the solubility of the protein in the acid beverage which then generates a large amount of insoluble particles in the acid beverage.
An advantage of using liquid soy protein is that the lower density, in comparison to the dry protein product, makes a more suspension stable acid beverage. The increased cost of transporting a liquid protein will be offset, in part, by the elimination of the spray drying step.
U.S. Pat. No. 3,995,071 (Goodnight, Jr. et al., Nov. 30, 1976) provides a process for the preparation of an improved purified soy protein having a low phytic acid content. A feature of this reference involves direct incorporation of the aqueous protein into special dietary and food products since it has been found that improved nutritional qualities, functionality (physical characteristics) and flavor are achieved when an aqueous protein is incorporated directly into the final composition as a liquid rather than employing an intermediate drying step prior to constitution with other ingredients.
U.S. Pat. No. 5,286,511 (Klavons et al., Feb. 15, 1994) provides a beverage such as orange juice that is clouded by a suspension of soy protein particles, where the protein particles are prevented from aggregating to the point of settling out by pectin. Pectin inhibits the protein from settling by adsorbing to individual protein particles and imparting an overall negative charge to the protein particles, resulting in repulsion of the particles from one another, and thereby preventing the protein particles from aggregating and settling out of the suspension. Pectin also increases the viscosity of the beverage, which helps stabilize protein particles against gravitational forces.
U.S. Pat. No. 6,221,419 (Gerrish, Apr. 24, 2001) relates to a pectin for stabilizing proteins particularly for use in stabilizing proteins present in aqueous acidified milk drinks. It must be understood that the inclusion of pectin has both desirable and undesirable effects on the properties of acidified milk drinks. While pectin can act as a stabilizer against sedimentation of casein particles or whey separation, it can have the disadvantage of increasing the viscosity of the drink due to its cross-linking with naturally co-present calcium cations rendering the drink unpalatable. It will be seen that in the absence of pectin, there is significant sedimentation in the case of both drinks caused by the instability of the casein particles which also results in relatively high viscosity. After a certain concentration of pectin has been added, the casein particles become stabilized against sedimentation after which increasing the pectin concentration has little effect on sedimentation. Turning to the viscosity of the drinks, this also significantly drops on stabilization of the casein particles but then almost immediately begins to rise again due to cross-linking of the excess pectin added by the co-present calcium cations. This increased viscosity is undesirable as it leads to the beverage having poor organoleptic properties. This range may be as narrow as only 0.06% by weight of pectin based upon the beverage weight as a whole. Below this working range, sedimentation is a significant problem, whereas above it, the viscosity of the beverage is undesirably high.